Intelligent Bag Filling For Exhaust Sampling System

ABSTRACT

An exhaust sampling system for an engine is provided. The exhaust sampling system may include a source of exhaust gas, an exhaust collection unit including at least one collection bag that selectively receives the exhaust gas, and a sample probe in fluid communication with the source of exhaust gas that selectively supplies the at least one collection bag with the exhaust gas. The exhaust sampling system may also include a controller that permits flow of the exhaust gas from the sample probe to the at least one collection bag in a first state and prevents flow of the exhaust gas from the sample probe to the at least one collection bag in a second state. The controller may determine an extraction rate of the sample probe based on an ON time of the engine during a test phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/402,623, filed on Nov. 20, 2014, which is a National Stage ofInternational Application No. PCT/US2013/042871, filed on May 28, 2013,which claims the benefit of U.S. Provisional Application No. 61/791,635,filed on Mar. 15, 2013 and claims the benefit of U.S. ProvisionalApplication No. 61/652,367, filed on May 29, 2012. The entire disclosureof each of the above applications is incorporated herein by reference.

FIELD

The present disclosure relates to an exhaust sampling system.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Exhaust sampling systems are conventionally used in conjunction withengines or vehicles with internal combustion engines to determine themass of pollutants produced by the engine during use. Such exhaustsampling systems may include a constant volume sampler (CVS) or a bagmini-diluter (BMD) that extract diluted exhaust gas for analysis in aneffort to determine the pollutant mass of the particular engine.

During operation of a CVS system, for example, engine exhaust is dilutedwith a diluent gas, and a sample of the diluted exhaust isproportionally extracted and stored in one or more sample bags.Depending on the engine or vehicle size, drive or duty cycle, andambient conditions, the CVS total flow rate, which includes both thediluent gas and engine exhaust, is selected to ensure the dilutedexhaust sample does not condense water when extracted during sampling,stored in the bags, or analyzed after the test phase. Once the samplebags are filled with diluted exhaust gas, the contents of the samplebags may be analyzed to determine the pollutant mass over the test phasefor the particular engine.

Vehicles incorporating traditional combustion engine powertrainscontinuously operate an internal combustion engine of the powertrainand, as a result, an internal combustion engine associated with aconventional vehicle powertrain is continuously operated during a testphase. As a result, collection of the diluted exhaust by the CVS systemis likewise continuous throughout the test phase.

New powertrains are being developed, however, that intermittently use aninternal combustion engine during operation of a vehicle. For example, ahybrid-electric vehicle may only use an internal combustion engine whenrecharging a battery of the vehicle. Such powertrains pose challengesfor both CVS sampling systems and BMD sampling systems, as each systemis conventionally configured to sample (i.e., collect) for analysis adiluted exhaust gas from an internal combustion engine that operatesduring an entire sample phase.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

An exhaust sampling system for an engine is provided. The exhaustsampling system may include a source of exhaust gas, an exhaustcollection unit including at least one collection bag that selectivelyreceives at least one of the exhaust gas, a diluent gas, and a mixtureof the exhaust gas and the diluent gas, and a first sample probe influid communication with the source of exhaust gas that selectivelysupplies the at least one collection bag with at least one of theexhaust gas, the diluent gas, and the mixture at an extraction rate. Theexhaust sampling system may also include a controller that permits theflow of at least one of the exhaust gas, the diluent gas, and themixture from the first sample probe to the at least one collection bagin a first state and prevents or bypasses the flow of at least one ofthe exhaust gas, the diluent gas, and the mixture from the first sampleprobe to the at least one collection bag in a second state. In oneexample, the controller determines the extraction rate of the firstsample probe during a test phase based on a time during said test phaseat which the engine is switched to an ON state.

In another configuration, an exhaust sampling system for an engine orvehicle is provided. The exhaust sampling system may include a dilutiontunnel in which exhaust gas from the engine is diluted with a diluentgas, an exhaust collection unit including at least one collection bagthat selectively receives the diluted exhaust gas, and a sample probe influid communication with the dilution tunnel and operable to selectivelysupply the at least one collection bag with the diluted exhaust gasduring a test phase, and a first flow path in fluid communication withsaid sample probe and said exhaust collection unit. The exhaust samplingsystem may also include a source of fill gas, a second flow path influid communication with said source of fill gas and said exhaustcollection unit, and a controller. At least a portion of said secondflow path may be different than said first flow path. The controller maybe operable to permit the flow of the diluted exhaust gas from thesample probe to the at least one collection bag in a first state andprevent or bypass the flow of the diluted exhaust gas from the sampleprobe to the at least one collection bag in a second state. Thecontroller may selectively supply said diluted exhaust gas to the atleast one collection bag through said first flow path during the testphase and selectively supply said fill gas to the at least onecollection bag through said second flow path during the test phase.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic view of a CVS sampling system in accordance withthe principles of the present disclosure;

FIG. 2 is a schematic view of a CVS sampling system in accordance withthe principles of the present disclosure;

FIG. 3 is a graph of exhaust flow and vehicle speed versus time for atest cycle of an internal combustion engine;

FIG. 4 is a graph of exhaust flow and vehicle speed versus time for atest cycle of an internal combustion engine that highlights when samplesof the exhaust gas are taken during the test cycle;

FIG. 5 is a graph of exhaust flow and vehicle speed versus time for atest cycle of an internal combustion engine that highlights asupplemental filling period performed during the test cycle; and

FIG. 6 is a schematic view of a BMD sampling system in accordance withthe principles of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

With reference to FIG. 1, an exhaust sampling system 10 is provided andmay include a dilution tunnel 12, an exhaust collection unit 14, abackground collection unit 16, a controller 18, and one or moreanalyzers 20. As will be described in greater detail below, the exhaustcollection unit 14 collects diluted exhaust gas from the dilution tunnel12 and provides a sample of the diluted exhaust gas to the analyzers 20to allow the analyzers 20 to determine a concentration of pollutants inthe diluted exhaust gas sample.

The dilution tunnel 12 may be fluidly coupled to an engine 22 and mayreceive a stream of exhaust gas from the engine 22. In oneconfiguration, the engine 22 is an internal combustion engine (ICE)configured for use in a vehicle having an electrically driven powertrain(neither shown). The dilution tunnel 12 may also be fluidly coupled to adiluent gas inlet 24 that provides diluent gas to the dilution tunnel12. As known in the art, the diluent gas provided to the dilution tunnel12 at the diluent gas inlet 24 may be ambient air. The diluent gas inlet24 may include a filter 26 that removes impurities from the air streamprior to the air stream entering the dilution tunnel 12.

A mixing plate 28 may be disposed within the dilution tunnel 12 and mayinclude an opening or aperture 30 formed therethrough. The aperture 30may cooperate with a body of the mixing plate 28 to cause air enteringthe dilution tunnel 12 at the inlet 24 to be mixed, as the air flowsthrough the aperture 30 of the mixing plate 28. Accordingly, exhaust gasfrom the engine 22 mixes with diluent gas received by the dilutiontunnel 12 at the diluent gas inlet 24 such that a substantiallyhomogeneous mixture of diluent gas and exhaust gas is received by a heatexchanger 32, which may be disposed downstream of the mixing plate 28.

The heat exchanger 32 may be located along a length of the dilutiontunnel 12 and may be used to maintain the mixture of exhaust gas anddiluent gas at a desired temperature. The temperature of the mixture maybe determined by a temperature sensor or other measuring device 34disposed downstream of the heat exchanger 32. In one example, themeasuring device 34 is a flowmeter that measures the flowrate of themixture. The flowmeter may also measure the temperature of the mixture.

A pump 36 may be fluidly coupled to the dilution tunnel 12 at anopposite end of the dilution tunnel 12 than the diluent gas inlet 24.The pump 36 may impart a fluid force on the dilution tunnel 12 to drawair into the diluent gas inlet 24 and through the filter 26. The forceimparted on the diluent gas inlet 24 causes diluent gas to enter thedilution tunnel 12 and mix with exhaust gas from the engine 22.Specifically, the force imparted on the diluent gas and on the exhaustgas from the engine 22 causes the exhaust gas and the diluent gas toencounter the mixing plate 28 and flow through the aperture 30. In sodoing, the diluent gas and the exhaust gas are mixed. Accordingly, asubstantially homogeneous mixture is received by the heat exchanger 32and by the measuring device 34. The homogeneous mixture of diluent gasand exhaust gas may then be expelled from the dilution tunnel 12 via anoutlet 38 of the pump 36.

With continued reference to FIG. 1, the exhaust collection unit 14 maybe fluidly coupled to the dilution tunnel 12 to receive a portion of thediluted exhaust gas (i.e., the homogeneous mixture of diluent gas andexhaust gas) disposed within and flowing through the dilution tunnel 12.The exhaust collection unit 14 may receive and store a portion of thediluted exhaust gas prior to the diluted exhaust gas being analyzed bythe analyzers 20.

The exhaust collection unit 14 may include one or more sample bags 40that store the diluted exhaust gas therein. The sample bags 40 may befluidly coupled to one or more sample probes that are in fluidcommunication with the dilution tunnel 12. As shown in FIG. 1, thesample probes may include a first sample probe 42, a second sample probe44, and a third sample probe 46. The sample probes 42, 44, 46 may beidentical such that the nozzles (not labeled) of each sample probe 42,44, 46 that receive the flow of diluted exhaust gas from within thedilution tunnel 12 are substantially equal. In other words, the nozzlesinclude substantially the same diameter such that the rate of flowreceived by each sample probe 42, 44, 46 is substantially identical.Conversely, the sample probes 42, 44, 46 may include different nozzlessuch that an inner diameter of each sample probe 42, 44, 46 isdifferent, thereby providing each sample probe 42, 44, 46 with adifferent sample extraction rate. Finally, while the sample probes 42,44, 46 may include different diameters and, thus, different extractionrates, two of the sample probes 42, 44, 46 may include the same diameterand, thus, the same extraction rate while the other of the three sampleprobes 42, 44, 46 includes a different diameter and, thus, a differentextraction rate. Regardless of the particular construction of thevarious sample probes 42, 44, 46, the sample probes 42, 44, 46 extract asample of the diluted exhaust gas from the dilution tunnel 12 andcommunicate the extracted sample of diluted exhaust gas to the samplebags 40 for storage.

Each of the sample probes 42, 44, 46 may be associated with a controlvalve that controls the flow of diluted exhaust gas from the sampleprobes 42, 44, 46 to the sample bags 40. Namely, the first sample probe42 may be fluidly coupled to a first control valve 48; the second sampleprobe 44 may be fluidly coupled to a second control valve 50; and thethird sample probe 46 may be fluidly coupled to a third control valve52. The control valves 48, 50, 52 control the flow of diluted exhaustgas respectively received by the sample probes 42, 44, 46 to the samplebags 40. The control valves 48, 50, 52 may be solenoid-actuated valves,for example, that are movable between an open state and a closed state.Alternatively, one or more of the control valves 48, 50, 52 may bestepper valves that are incrementally movable from a fully open state toa closed state. In other words, one or more of the control valves 48,50, 52 are variable valves having any number of open states between thefully open state and the fully closed state to provide a degree ofadjustability to one or more of the valves 48, 50, 52. Accordingly, ifone or more of the control valves 48, 50, 52 includes a stepper valve,the control valves 48, 50, 52 may meter the flow of diluted exhaust gasfrom the dilution tunnel 12 to the sample bags 40 to finely control theextraction rate of the diluted exhaust gas and, ultimately, the amountof diluted exhaust gas received by the sample bags 40 during a testinterval or test phase.

Diluted exhaust gas may be received by the sample probes 42, 44, 46 andmay be drawn through the control valves 48, 50, 52 by a pump 54.Specifically, the pump 54 may be disposed downstream of the controlvalves 48, 50, 52 and may impart a force on the sample probes 42, 44, 46to cause diluted exhaust gas to be drawn into the sample probes 42, 44,46 and to flow through the control valves 48, 50, 52.

The diluted exhaust gas drawn through the control valves 48, 50, 52 mayalso flow through a flow meter 56 prior to being received by the samplebag 40. The diluted exhaust gas may be received by one or more of thesample bags 40, whereby flow of the diluted exhaust gas into therespective sample bags 40 is controlled by a control valve 58 disposedupstream of each of the sample bags 40. As indicated above, the sampleprobes 42, 44, 46 may be replaced with a single sample probe, and thecontrol valves 48, 50, 52 may be replaced with a single control valve.For example, the control valves 48, 50, 52 may be replaced with a flowcontrol device such as a mass flow controller which, as known in theart, includes a control valve and a flow meter. Since the mass flowcontroller includes a flow meter, the flow meter 56 may be omitted inthese implementations.

While the sample bags 40 are described and shown as receiving dilutedexhaust gas from the dilution tunnel 12 via the sample probes 42, 44, 46and control valves 48, 50, 52, the sample bags 40 may additionallyreceive fill gas 60 at any point during a test interval or test phase.The fill gas 60 may be drawn through a flow meter 62 by a pump 64 priorto being received by the sample bags 40. The fill gas 60 may flowthrough a control valve 66 prior to reaching the flow meter 62 and mayflow through a control valve 68 prior to being received by the samplebags 40. The control valve 66 may be selectively moved between an openstate permitting flow of fill gas 60 to the flow meter 62 and a closedstate preventing flow of fill gas 60 to the flow meter 62. The fill gas60 is permitted to enter the sample bags 40 when the control valve 68 isan open state and is prevented from entering the sample bags 40 when thecontrol valve 68 is in a closed state.

As shown in FIG. 1, the controller 18 may be in communication with theflow meter 62, the pump 64, and the control valve 66 to control theamount of fill gas 60 supplied to the sample bags 40 during a testinterval or test phase. For example, if the amount of diluted exhaustgas received by the sample bags 40 during a test interval or test phaseis insufficient to allow the analyzers 20 to determine the concentrationof pollutants contained within the exhaust gas, the controller 18 mayenergize the pump 64 and may open the control valve 66 to supply thesample bags 40 with a volume of fill gas 60. The fill gas 60 mixes withthe diluted exhaust gas disposed within the sample bags 40 and serves tosupplement the volume disposed within each sample bag 40. Further, thefill gas 60 may be a clean, dry gas that reduces the likelihood ofcondensation forming within the sample bags 40. Additionally oralternatively, the fill gas 60 may be the diluent gas provided to thedilution tunnel 12 at the diluent gas inlet 24.

The background collection unit 16 may be used by the analyzers 20 whendetermining the concentration of pollutants contained within the dilutedexhaust gas provided by the exhaust collection unit 14. Specifically,the analyzers 20 may analyze a sample of the diluent gas provided to thedilution tunnel 12 at the diluent gas inlet 24 and account for anybackground contaminates within the diluent gas supplied at the diluentgas inlet 24.

The background collection unit 16 may include one or more sample bags70, a pump 72, and a flow control device such as a control valve 74. Thepump 72 may draw diluent gas from the filter 26 through the controlvalve 74 when the control valve 74 is in an open state. The diluent gasdrawn from the filter 26 by the pump 72 may be directed through a flowmeter 76 prior to being received by the sample bags 70. The diluent gasmay flow through the flow meter 76 and may be received by the samplebags 70 for collection. The sample bags 70 may be respectivelyassociated with control valves 78 that selectively permit the flow ofdiluent gas into one or more of the sample bags 70.

With continued reference to FIG. 1, the analyzers 20 is shown as beingfluidly coupled to the exhaust collection unit 14 and as being fluidlycoupled to the background collection unit 16. Accordingly, the analyzers20 may receive a diluted exhaust gas sample from the exhaust collectionunit 14 and may receive a diluent gas sample from the backgroundcollection unit 16.

The analyzers 20 may receive a sample of diluted exhaust gas from theexhaust collection unit 14 and/or may receive a sample of diluent gasfrom the background collection unit 16 by imparting a force on the fluidcontained within the units 14, 16 via a pump 80. The pump 80 may drawdiluted exhaust gas from the exhaust collection unit 14 when one or morecontrol valves 82 associated with the exhaust collection unit 14 are inan open state. Likewise, the pump 80 may draw diluent gas from thebackground collection unit 16 when one or more control valves 84associated with the background collection unit 16 are in an open state.The diluted exhaust gas sample or diluent gas sample may be drawn fromthe respective units 14, 16 and may flow through a control valve 86 andflow meter 88 prior to reaching the analyzers 20. Once the analyzers 20receive the diluted exhaust gas sample from the exhaust collection unit14 and/or the diluent gas sample from the background collection unit 16,the analyzers 20 may determine the concentration of pollutants containedwithin the diluted exhaust gas sample, which may be used along withvolume measurements to determine the mass of pollutants produced by theengine.

With continued reference to FIG. 1, operation of the exhaust samplingsystem 10 will be described in detail. The following operation of theexhaust sampling system 10 may be performed by the controller 18. Whilenot specifically illustrated in FIG. 1, the controller 18 may be incommunication with the measuring device 34, the pumps 36, 54, 64, 72,80, the control valves 48, 50, 52, 58, 66, 68, 74, 82, 84, 86, and theflow meters 56, 62, 76. Accordingly, the controller 18 may receiveoperating data from the measuring device 34 and from the flow meters 56,62, 76, and may use the foregoing information to control the pumps 36,54, 64, 72, 80 and the control valves 48, 50, 52, 58, 66, 68, 74, 82,84, 86 in an effort to allow the analyzers 20 to obtain an accuratereading of the concentration of pollutants contained within the dilutedexhaust gas disposed within the dilution tunnel 12.

The controller 18 may be programmed to run any number of test procedureshaving any number of test intervals or test phases. For example, thecontroller 18 may sample diluted exhaust gas from the dilution tunnel 12during a test phase of five hundred and five seconds (505 s) bycontrolling the various pumps 36, 54, 64, 72, 80 and control valves 48,50, 52, 58, 66, 68, 74, 82, 84, 86. A test phase is that portion of atest procedure during which exhaust gas is collected in one or more ofthe sample bags 40. A test procedure may include multiple test phases,and exhaust gas may be collected in a different one of the sample bags40 during each one of the test phases. For example, the U.S.Environmental Protection Agency Federal Test Procedure (40 CFR 1066.815)includes a cold transient phase, a cold stabilized phase, a hottransient phase, and a hot stabilized phase, and exhaust gas iscollected in different sample bags during each of these four testphases. Thus, in exhaust sample systems that add fill gas prior to orfollowing a test phase, fill gas may be added to one sample bag during atest phase in which exhaust gas is collected in another sample bag.However, discussions herein regarding adding diluent gas and/or fill gasto a sample bag “during a test phase” refer exclusively herein, as wellas in the claims, to adding diluent gas and/or fill gas to a sample bagduring the same test phase in which exhaust gas is collected in thatsample bag. While any number of test procedures may be performedincluding test phases having virtually any length, the followingdescription will be made with reference to an exemplary test phasehaving a length of five hundred and five seconds (505 s).

The controller 18 may initiate a test phase at a zero time. If at thezero time the engine 22 is not running, the controller 18 may move thevalves 48, 50, 52 into the open state and may energize the pump 54 tovent the diluent gas drawn from the dilution tunnel 12. Specifically,the controller 18 may open a valve 57 downstream of the pump 54 to ventthe diluent gas drawn from the dilution tunnel 12 when the engine 22 isin the OFF state. The controller 18 may also ensure that the sample bags40 are completely empty by opening a valve 89 and energizing a pump 90that may be used to evacuate any air disposed within the sample bags 40prior to initiation of the test phase.

The controller 18 may maintain the pump 54 in the energized state andthe valves 48, 50, 52 in the open state while the engine 22 is in theOFF state. The controller 18 may likewise maintain the pump 72 in theenergized state and the valve 74 in the open state when the engine 22 isin the OFF state. As with the diluent gas extracted from the dilutiontunnel 12 by the sample probes 42, 44, 46 when the engine 22 is in theOFF state, the diluent gas extracted by the pump 72 when the engine 22is in the OFF state may be vented by opening a valve 73 disposeddownstream from the pump 72.

The controller 18 may be in communication with a sensor 92 that monitorsoperation of the engine 22. Additionally or alternatively, thecontroller 18 may receive the state of the engine 22 (i.e., ON or OFF)from another system such as a computer or controller that controls thetest cycle (i.e., a test-automation system) or from a CAN bus or OBD(on-board data) of a vehicle under test. For example, as known in theart, the controller 18 may determine the state of the engine 22 based ona flow rate of exhaust gas flowing through a tailpipe of the engine 22,a pressure of exhaust gas flowing through the tailpipe, and a change inpressure of diluted exhaust gas flowing through the dilution tunnel 12.Regardless of how the controller 18 determines the state of the engine22, the controller 18 may maintain the valves 57, 73 in the open stateuntil the controller 18 receives a signal from the sensor 92 that theengine 22 is in the ON state. At this point, the controller 18 may closethe valves 57 to prevent venting of the diluted exhaust gas extractedfrom the dilution tunnel 12 and close the valve 73 to prevent venting ofthe diluent gas extracted from the dilution tunnel 12. The engine 22 isin the ON state anytime the engine 22 produces exhaust gas, which mayinclude periods when the engine 22 is cranking, the engine 22 isrunning, and/or a brief (e.g., 5 second) period after the engine 22stops running.

The controller 18 may record the time—during the test interval or testphase—at which the engine 22 turns ON, as reported by the sensor 92.Namely, the controller 18 may determine the time from the zero timerecorded at the beginning of the test phase to determine how much timehas elapsed during the test phase prior to the engine turning ON. Thecontroller 18 may record and utilize the ON time of the engine 22 toensure a sufficient volume is collected by the sample bags 40 at adesired dilution ratio, as will be discussed in greater detail below.

The controller 18 may determine the sample flow rate for the sample bags40 based on the size of the sample bags 40. Namely, the controller 18may determine the sample flow rate that would be required to fill thesample bags 40 if the engine 22 is running during the entire test phase.The sample fill flow rate may be determined by the length of thecollection period (i.e., five hundred and five seconds in the presentexample) and the volume of the sample bags 40. The sample fill flow ratemay be determined by dividing the volume of the sample bags 40 (i.e.,the max target fill volume) by the length of the test phase (fivehundred and five seconds).

As thus far described, the controller 18 only closes the valves 57, 73when the engine 22 is moved into the ON state, as indicated by thesensor 92. When the engine 22 is not running (i.e., is in an OFF state),the valves 57, 73 are in the open state to vent diluent gas collectedfrom the dilution tunnel 12. Accordingly, when the engine 22 is in theOFF state and the valves 57, 73 are in the open state, the exhaustcollection unit 14 and the background collection unit 16 do not collecta sample within the respective sample bags 40, 70.

If the engine 22 is in the ON state for the entire test phase, thecontroller 18 may simultaneously energize the pumps 54, 72 and open thevalves 48, 50, 52, 74 to allow the sample bags 40 of the exhaustcollection unit 14 and the sample bags 70 of the background collectionunit 16 to respectively collect a diluted exhaust gas sample and adiluent gas sample. The pumps 54, 72 will remain energized and thevalves 48, 50, 52, 74 will remain open—provided the engine 22 remains inthe ON state.

When the sensor 92 indicates that the engine 22 is in the ON state, thecontroller 18 determines the flow rate required to allow the sample bags40 of the exhaust collection unit 14 and the sample bags 70 of thebackground collection unit 16 to receive a sufficient volume of dilutedexhaust gas and diluent gas, respectively. Alternatively, the controller18 can continuously calculate and adjust the flow rate until the sensor92 indicates that the engine 22 is in the ON state.

In order to allow the analyzers 20 to analyze the diluted exhaust gassample received from the exhaust collection unit 14 and to analyze thediluent gas sample received from the background collection unit 16, thesample bags 40 of the exhaust collection unit 14 must receive asufficient volume of diluted exhaust gas and the sample bags 70 of thebackground collection unit 16 must receive a sufficient volume ofdiluent gas. The volume of diluted exhaust gas received by the samplebags 40 of the exhaust collection unit 14 is determined based on theextraction rate of diluted exhaust gas from the dilution tunnel 12 bythe sample probes 42, 44, 46. Because the controller 18 only opens thevalves 58 to collect diluted exhaust gas from the dilution tunnel 12when the engine 22 is in the ON state, an insufficient volume of dilutedexhaust gas may be collected if the engine 22 is only in the ON statefor a short time during the five hundred and five second (505 s) testphase.

The controller 18 ensures that sampling of the diluted exhaust gas fromthe dilution tunnel 12 achieves the minimum volume required by theanalyzers 20—regardless of the state of the engine 22 (i.e., ON or OFF).In short, the controller 18 maintains the valves 58, 78 in the closedstate and the bypass valves 57, 73 in the open state until a point intime during the test phase in which the valves 58, 78 must be opened andthe bypass valves 57, 73 closed to achieve the minimum volume requiredby the analyzers 20. In other words, even if the engine 22 is in the OFFstate but a predetermined amount of time has passed since the start ofthe test phase, the controller 18 may close the bypass valves 57, 73 andmay open the valves 58, 78 to allow the sample bags 40 to be filled withdiluent gas flowing through the dilution tunnel 12 and to allow thesample bags 70 to be filled with diluent gas.

Additionally or alternatively, the controller 18 may maintain the pump54 in the energized state and may maintain the valves 48, 50, 52 and thebypass valve 57 in the open state, and may open the valves 66, 68 andenergize the pump 64 to cause fill gas 60 to enter the sample bags 40.Accordingly, the sample bags 40 may be filled with fill gas 60 duringthe test phase. While the controller 18 is described as filling thesample bags 40 with diluent gas from the dilution tunnel 12 or with fillgas 60, the controller 18 could fill the sample bags 40 with bothdiluent gas from the dilution tunnel 12 and with fill gas 60. Again, thecontroller 18 may at least partially fill the sample bags 40 withdiluent gas from the dilution tunnel 12 or with fill gas 60 to allow thesample bags 40 to achieve a minimum volume required by the analyzers 20to analyze the contents within the sample bags 40. The minimum samplevolume required by the analyzers 20 may be predetermined by propertiesof the analyzers 20 such as the flow rate of the analyzers 20 as well asby the required analysis time. In sum, the controller 18 may provide thesample bags 40 with either or both of diluent gas from the dilutiontunnel 12 or fill gas 60 during the test phase.

Adding diluent gas from the dilution tunnel 12 and/or fill gas 60 to thesample bags 40 during the test phase increases the efficiency of theexhaust sampling system 10, as such diluent gas and/or fill gas 60 isnot added prior to or following the test phase. Accordingly, adding thediluent gas from the dilution tunnel 12 and/or fill gas 60 during thetest phase streamlines the overall test, as the gas added to the samplebags 40 is added during the test phase and is not required as anadditional step either prior to or following the test phase.

At the beginning of the test phase, the controller 18 determines asample extraction rate for the sample probes 42, 44, 46 based on thevolume of the sample bags 40, and the prescribed collection time (i.e.,the length of the test phase). The extraction rate determined by thecontroller 18 at the start of the test phase may be the initialextraction rate and may be limited by the length of the test phase. Forexample, the sample bags 40 include a fixed or maximum volume.Accordingly, longer test phases require the controller 18 to select anextraction flow rate that, when integrated, will not exceed the volumeof the sample bags 40.

During operation, the controller 18 may adjust the extraction rate ofthe probes 42, 44, 46 based on operation of the engine 22. Namely, thecontroller 18 may continuously calculate the extraction rate required toprovide the sample bags 40 with a desired volume based on the timeduring the test phase in which the engine 22 is moved to the ON state.When the engine 22 is first moved into the ON state, the extraction flowrate is selected and is maintained until the end of the test phase toensure proportional sampling, which is required by the proportionalsampling theory of CVS and BMD systems for accurately calculating thepollutant mass contained within the diluted exhaust gas sample.

Based on the foregoing, the controller 18 may optimize the initialextraction rate by continuously calculating the extraction rate untilthe engine 22 is moved to the ON state, as identified by the sensor 92.Accordingly, the controller 18 ensures that the extraction rate selectedprovides the sample bags 40 with the desired volume, thereby allowingthe controller 18 to achieve a sufficient volume of diluted exhaust gasrequired by the analyzers 20. However, the sample bags 40 may notcollect a sufficient volume of diluted exhaust gas for the analyzers 20if the diluted exhaust gas is only extracted from the dilution tunnel 12at the selected extraction rate during periods when the engine 22 is inthe ON state. If the controller 18 recognizes this condition, thecontroller 18 may provide diluent gas from the dilution tunnel 12 to thesample bags 40 at the selected extraction rate when the engine 22 is inthe OFF state.

Adjusting the extraction flow rate likewise minimizes the need for thecontroller 18 to supply the sample bags 40 with diluent gas from thedilution tunnel 12 and/or with fill gas 60 to provide the analyzers 20with the minimum volume required. The controller 18 may continuouslycalculate and optimize the extraction flow rate of the sample probes 42,44, 46—prior to the engine 22 moving into the ON state—to adjust theextraction flow rate such that a sufficient sample is taken when theengine 22 is in the ON state, thereby minimizing or eliminating the needto fill the sample bags 40 with diluent gas from the dilution tunnel 12or with fill gas 60 when the engine 22 is in the OFF state. Accordingly,the sample bags 40 are filled primarily with diluted exhaust gas fromthe dilution tunnel 12 and, as a result, the dilution ratio of thesample contained within the sample bags 40 is minimized.

The controller 18 may achieve the extraction flow rate by controllingone or more of the valves 48, 50, 52. For example, if the sample probes42, 44, 46 include different sized nozzles such that the first sampleprobe 42 provides an extraction flow rate of approximately two (2) lpm(liters per minute), the second sample probe 44 provides an extractionflow rate of approximately five (5) lpm, and the third sample probe 46provides an extraction flow rate of approximately five (5) lpm, thecontroller 18 may only open the valves 48, 50 associated with the firstsample probe 42 and the second sample probe 44 if the calculatedextraction flow rate is approximately seven (7) lpm. Because the firstsample probe 42 includes an extraction sample rate of approximately two(2) lpm and the second sample probe 44 supplies an extraction flow rateof approximately five (5) lpm, use of the first sample probe 42 and thesecond sample probe 44 provides a total sample extraction flow rate ofapproximately seven (7) lpm.

If, on the other hand, the controller 18 determines that a higher sampleextraction flow rate is required (i.e., if the engine 22 is moved to theON state later during the test phase) such that a sample extraction flowrate of approximately twelve (12) lpm is required, the controller 18 mayopen each of the valve 48, 50, 52 to allow the extraction flow rateprovided by the sample probes 42, 44, 46 to equal approximately twelve(12) lpm (i.e., two (2) lpm from sample probe 42; five (5) lpm fromsample probe 44; and five (5) lpm from sample probe 46).

The foregoing example illustrates how the controller 18 may adjust thesample extraction flow rate by controlling the valves 48, 50, 52 andonly permitting flow through selective ones of the sample probes 42, 44,46 when the engine 22 is moved to the ON state. Regardless of how thesample extraction flow rate is achieved, once the controller 18determines the sample extraction rate, the sample extraction rate ismaintained throughout the test phase and is determined based on when theengine 22 is moved into the ON state during the test phase. If pulsewidth modulation (PWM) is used to control one or more of the valves 42,44, 46, proportional sampling is maintained with the flow meter 56functioning as a feedback element.

The pollutant mass (m) over the test phase may be determined based onthe pollutant concentration of the proportionally collected exhaustsample and the respective integrated CVS volume. See Equation 1 below.

m=V _(mix)*ρ_([pollutant]) *c*x  (1)

In the foregoing equation, m represents the pollutant mass in grams overthe test phase; V_(mix) represents the total dilute exhaust volume overthe test phase at standard reference conditions (scf or m³);ρ[pollutant] represents the density of the appropriate chemical species(g/scfm or gram/m³); x represents the measured pollutant concentrationin the sample after dry-to-wet and background corrections (ppmV orpercent); and c represents ten-two for pollutant concentrationspercentage and ten-six for pollutant concentrations in ppm.

Based on the foregoing, integration of the CVS flow rate to determinethe CVS volume must be started and stopped in conjunction with fillingof the sample bags 40, 70. Accordingly, the controller 18 may start andstop integration of the CVS flow rate to determine the CVS volume inEquation 1 in conjunction with starting and stopping of bag filling(i.e., filling of the sample bags 40, 70).

The controller 18 may likewise sequence filling of the sample bags 70associated with the background collection unit 16 with filling of thesample bags 40 associated with the exhaust collection unit 14.Accordingly, when the controller 18 opens the valves 58 or provides thesample bags 40 with diluent gas and/or fill gas 60, the controller 18likewise may open valves 78 to fill the sample bags 70 with diluent gas.In short, the sample bags 70 may be filled at the same time as thesample bags 40 such that the sample bags 70 are controlled in the samemanner as the sample bags 40.

While the sample bags 70 are described as being controlled in the samemanner as the sample bags 40 such that the sample bags 70 are filledwith diluent gas at the same time the sample bags 40 are filled withdiluted exhaust gas, diluent gas, or fill gas 60, the sample bags 70could be controlled in a different manner. Namely, the sample bags 70may collect diluent gas during the entire test phase. Alternatively, thevolume of the collected diluent gas within the sample bags 70 may beadjusted with clean gas in a similar manner as the fill gas 60 issupplied to the sample bags 40 to ensure that the volume containedwithin the sample bags 70 achieves a minimum volume required foranalysis by the analyzers 20.

In sum, the controller 18 controls the exhaust sampling system 10 toachieve a desired (i.e., low) dilution ratio by starting and stoppingfilling of the sample bags 40 with diluted exhaust gas in conjunctionwith engine ON/OFF times. Further, the controller 18 achieves a targetvolume within the sample bags 40 by selectively adding diluent gas fromthe dilution tunnel 12 and/or fill gas 60 to the sample bags 40 duringthe test phase. The controller 18 may also select the extraction flowrate achieved by the sample probes 42, 44, 46 and may continually adjustthe extraction sample rate during the test phase until the engine 22 ismoved to the ON state. Finally, the controller 18 may control the flowof diluent gas into the sample bags 70 such that diluent gas is receivedby the sample bags 70 at the same time that diluted exhaust gas, diluentgas, or fill gas 60 is received by the sample bags 40.

As described above, the controller 18 may control the exhaust samplingsystem 10 such that the sample bags 40 are selectively filled withdiluent gas from the dilution tunnel 12 and/or fill gas 60 if the volumeof diluted exhaust gas received by the sample bags 40 is insufficient toallow the analyzers 20 to properly analyze the contents of the samplebags 40. The foregoing system 10 may be simplified by removing thesource of fill gas 60 such that the controller 18 only fills the samplebags 40 with diluent gas from the dilution tunnel 12 should the samplebags 40 receive an insufficient volume of diluted exhaust gas during atest phase.

A schematic representation of an exhaust sampling system 10 a having thesource of fill gas 60 removed is shown in FIG. 2. In view of thesubstantial similarity in structure and function of the componentsassociated with the exhaust sampling system 10 with respect to theexhaust sampling system 10 a, like reference numerals are used toidentify like components while like reference numerals containing letterextensions are used to identify those components that have beenmodified.

Operation of the exhaust sampling system 10 a is virtually identical tothe exhaust sampling system 10 with the exception that the controller 18only supplies the sample bags 40 with diluent gas from the dilutiontunnel 12 when the volume of diluted exhaust gas supplied to the samplebags 40 is insufficient to allow the analyzers 20 to properly analyzethe contents of the sample bags 40. Operation of the exhaust samplingsystem 10 a is otherwise identical to operation of the exhaust samplingsystem 10. Accordingly, a detailed description of the operation of theexhaust sampling system 10 a is foregone.

The foregoing systems 10, 10 a optimize bag filling of a CVS system tooptimize the dilution ratio of the sample(s) taken, provide enoughsample in the collection bags 40 for analysis, and achieve the foregoingobjectives within a defined sampling phase time. The systems 10, 10 aextract samples in parallel with operation of the engine 22 andsupplement the volume of the collection bags 40 when a minimum samplevolume required for analysis would not be achieved. The supplementedvolume may be provided to the collection bags 40 during the test phasewhen the engine 22 is in the OFF state.

One approach to achieve a minimum sample volume required for analysis isto integrate the bag sample volume during a test interval (i.e., testphase) and to determine the point in the test interval that samplecollection is required to remain ON—for the remainder of the testinterval—to achieve the minimal sample volume necessary for analysis.FIGS. 3-5 provide an example of the foregoing approach.

With reference to FIG. 3, a test interval for an engine 22 is provided.The test interval includes a run time of five hundred and five seconds(505 s) with the engine 22 only in the ON state for 191 seconds duringthe test interval.

If a CVS flow rate of 350 scfm is selected, the results shown below inTable 1 represent CVS standard operation. The overall dilution ratio ishigh but the system would have enough sample in the collection bag 40for analysis.

TABLE 1 CVS Integrated Collection Integrated Flow (cfm Bag Sample Basedon Dilution Volume Example Time 350 scfm) Ratio (liters) CVS Standard505 2945.8 27.7 90.0 Operation

In the above test, sampling may be optimized by only collecting a samplewhen the engine 22 is in the ON state. Namely, CVS bag sampling is onlyperformed during the times of the test interval that the engine 22 is inthe ON state and, as a result, the system would only collect a bagsample for 191 seconds, as shown below in Table 2. The sample periodsfor optimized bag sampling (i.e., only sampling when the engine 22 is inthe ON state) are shown in FIG. 4.

TABLE 2 CVS Integrated Collection Integrated Flow (cfm Bag Sample Basedon Dilution Volume Example Time 350 scfm) Ratio (liters) CVS Standard505 2945.8 27.7 90.0 Operation Optimized Bag 191 1114.17 10.48 34.0Sampling

While the dilution ratio of the sample is improved by only extracting asample during periods when the engine 22 is in the ON state, thecollected volume often does not yield a sufficient sample required foranalysis.

As described above, the collection bag 40 may be filled at some pointduring the test interval when the engine is in the OFF state. In FIG. 5,this period is shown at the end of the test interval. Namely, if atarget sample volume is established in order to have enough sample toanalyze, the control system—based on the amount of exhaust gas alreadycollected—can recognize the point in time during the test interval whensampling will have to be turned on for the remainder of the testinterval in order to collect the desired volume by the end of the testinterval.

As shown below in Table 3, by filling the collection bag 40 withadditional diluent gas or fill gas during the test interval when theengine 22 is in the OFF state, the sample volume for analysis isincreased from 34 liters to 41.5 liters. At the same time, the dilutionratio is maintained at the lowest possible ratio consistent withobtaining enough sample to analyze.

TABLE 3 CVS Integrated Collection Integrated Flow (cfm Bag Sample Basedon Dilution Volume Example Time 350 scfm) Ratio (liters) CVS Standard505 2945.8 27.7 90.0 Operation Optimized Bag 191 1114.17 10.48 34.0Sampling Optimized Bag 233 1359.17 12.79 41.5 Sampling With SupplementalBag Filling

Employing optimized bag sampling (i.e., only sampling when the engine 22is in the ON state) and providing supplemental bag filling at a selectedtime during the test interval when the engine 22 is in the OFF stateallows the CVS system to achieve a minimum sample volume required foranalysis while optimizing the dilution ratio of the sample. Further,supplementing bag fill during the test interval avoids implementation ofpre-dilution or post-dilution procedures (i.e., supplementing bag fillprior to or following the test interval). Finally, existing CVS systemsmay be upgraded to perform the foregoing procedure without additionalhardware.

With particular reference to FIG. 6, another exhaust sampling system 100is provided. The exhaust sampling system 100 provides a BMD samplingsystem, whereby an exhaust sample is diluted at a fixed dilution ratioand is collected in proportion to an exhaust flow from an engine 102. Inthe schematic shown in FIG. 6, the engine 102 includes an internalcombustion engine 104 and another engine 106 such as an electric motorthat cooperate to provide a propulsion unit for a hybrid vehicle (notshown). The engine 106 may be the primary propulsion unit of the vehicleand, as a result, there may be periods of operation of the vehicle whenthe internal combustion engine 104 expels little or no exhaust through atailpipe 108 of the engine 104.

The exhaust sampling system 100 may include a sampling unit 110, anexhaust collection unit 112, a controller 114, and an analyzer 116. Thesampling unit 110 may be in fluid communication with a sample probe 118and may include a mixer 120. The sample probe 118 may be received withinthe tailpipe 108 to allow the sample probe 118 to collect a sample ofexhaust gas from the engine 102. The sample of exhaust gas may be drawninto the sampling unit 110 by a pump 122 and may be measured by a flowmeter 124 disposed between the sample probe 118 and the pump 122.

The exhaust collection unit 112 may be in fluid communication with thesampling unit 110 and may include one or more sample bags 126 and a pump128 that draws a sample of diluted exhaust gas into the sample bags 126.The diluted exhaust gas may be drawn from the sampling unit 110, wherethe exhaust gas received from the sample probe 118 is mixed with adiluent gas 130. Specifically, the diluent gas 130 may flow through aflow meter 132 and may subsequently be received by the mixer 120 of thesampling unit 110. The mixer 120 may mix the diluent gas 130 with theexhaust gas sample received from the sample probe 118 to create a sampleof diluted exhaust gas. The diluted exhaust gas may be drawn from thesampling unit 110 by the pump 128 and may be collected by the samplebags 126 of the exhaust collection unit 112. Collection of the dilutedexhaust gas by the sample bags 126 may be controlled by a pair ofcontrol valves 134 respectively associated with each of the sample bags126.

The analyzer 116 may receive a sample of diluted exhaust gas from thesample bags 126 for analysis. Specifically, a pump 136 may draw a sampleof diluted exhaust gas from the sample bags 126 and may pump the dilutedexhaust gas sample through a control valve 138 and a flow meter 140prior to the diluted exhaust gas sample reaching the analyzer 116. Theanalyzer 116 may analyze the diluted exhaust gas to determine theconcentration of pollutants contained within the exhaust gas.

As with the exhaust sampling systems 10, 10 a, the sample bags 126 mustinclude a sufficient volume to allow the analyzer 116 to properlyanalyze the diluted exhaust gas sample. If the diluted exhaust gassample received from the sampling unit 110 is insufficient to fill thesample bags 126, fill gas 142 may be provided to one or more of thesample bags 126 via a flow meter 144 and control valve 146.

With continued reference to FIG. 6, operation of the exhaust samplingsystem 100 will be described in detail. As with the exhaust samplingsystems 10, 10 a, any number of tests may be performed using the exhaustsampling system 100 and, further, any of the tests may include testintervals or test phases having virtually any duration. While theexhaust sampling system 10 may be used in conjunction with numeroustests and in conjunction with test intervals or test phases of virtuallyany length, an exemplary test phase of five hundred and five seconds(505 s) will be described hereinafter.

The controller 114 may be in communication with a sensor 148 or 152 thatidentifies the state of the engine 102. Namely, the sensor 148identifies whether the engine 102 is in an ON state or an OFF state. Ifsensor 152 is used, the sensor 152 measures the ON or OFF state bymeasuring the exhaust flow. Regardless of the state of the engine 102,the controller 114 instructs the pump 122 into an energized state todraw an exhaust gas sample into the sampling unit 110 via the sampleprobe 118. The exhaust gas sample may be mixed with the diluent gas 130by the mixer 120 to produce a sample of diluted exhaust gas. A mass flowcontroller 150 may be in communication with an exhaust flow meter 152and may control an amount of diluted exhaust gas supplied to the samplebags 126. If the engine 102 is in the ON state, the diluted exhaust gasis received within the collection bags 126 due to the controller 114opening the valves 134. If, on the other hand, the engine 102 is in theOFF state, the controller 114 may close the valves 134 and open a bypassvalve 129. The controller 114 may also energize a pump 131 locateddownstream of the valve 129 to vent the diluted exhaust gas. In variousimplementations, the bypass valve 129 and the pump 131 may be omitted,and the controller 114 may simply close the valves 134 when the engine102 is in the OFF state.

As with the exhaust sampling systems 10, 10 a, if the volume of dilutedexhaust gas supplied to the sample bags 126 is insufficient to achievethe minimum volume required, fill gas 142 may be added to the samplebags 126 during the test interval or test phase. The controller 114 maydetermine whether the volume of diluted exhaust gas supplied to thesample bags 126 is insufficient to achieve the minimum volume based onpredetermined characteristics such as the ON/OFF behavior of the engine104, the exhaust flow behavior of the engine 104, and the test phasecharacteristics. Adding fill gas 142 to the sample bags 126 during thetest interval or test phase increases the efficiency of the exhaustsampling system 100, as additional procedures either before the testphase or after the test phase are not required. Specifically, addingfill gas 142 to the sampling bags 126 prior to or following the testphase is not required, as the fill gas 142 is added during the testphase.

Once the sample bags 126 are filled with a sufficient volume of dilutedexhaust gas, control valves 154 associated with the exhaust collectionunit 112 may be opened to permit the analyzer 116 to receive a sample ofdiluted exhaust gas for analysis.

While the controller 114 is not shown in communication with eachcomponent of the exhaust sampling system 100, the controller 114 may bein communication with the sensor 148; the pumps 122, 128, 136; thecontrol valves 138, 146, 154; the flow meters 124, 132, 140, 144, 152;and the mass flow controller 150. Accordingly, the controller 114 maycontrol the pumps 122, 128, 136 and control valves 138, 146, 154 basedon information received from the sensor 148 and the various flow meters124, 132, 140, 144, 152.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. An exhaust sampling system for an engine, theexhaust sampling system comprising: a source of exhaust gas; an exhaustcollection unit including at least one collection bag that selectivelyreceives at least one of said exhaust gas, a diluent gas, and a mixtureof said exhaust gas and said diluent gas; a sample probe in fluidcommunication with said source of exhaust gas and operable toselectively supply said at least one collection bag with at least one ofsaid exhaust gas, said diluent gas, and said mixture at an extractionrate; and a controller operable to permit the flow of at least one ofsaid exhaust gas, said diluent gas, and said mixture from said sampleprobe to said at least one collection bag in a first state and operableto prevent the flow of at least one of said exhaust gas, said diluentgas, and said mixture from said sample probe to said at least onecollection bag in a second state, said controller determining saidextraction rate of said sample probe during a test phase based on a timeduring said test phase at which the engine is switched to an ON state.2. The exhaust sampling system of claim 1, further comprising a valveassociated with said sample probe and movable between an open statepermitting flow of at least one of said exhaust gas, said diluent gas,and said mixture to said at least one collection bag and a closed statepreventing flow of at least one of said exhaust gas, said diluent gas,and said mixture to said at least one collection bag, said controller incommunication with said valve and operable to control movement of saidvalve between said open state and said closed state.
 3. The exhaustsampling system of claim 2, wherein said open state is a fully openstate, and said valve is movable into one of a plurality of partiallyopen states between said fully open state and said closed state.
 4. Theexhaust sampling system of claim 1, further comprising a source of fillgas, wherein said controller is operable to selectively supply said fillgas to said at least one collection bag.
 5. The exhaust sampling systemof claim 4, wherein said source of fill gas is separate from said sourceof exhaust gas.
 6. The exhaust sampling system of claim 4, wherein saidexhaust gas is extracted from a tunnel containing said mixture of saidexhaust gas and said diluent gas when the engine is in said ON state,said source of fill gas being said diluent gas when the engine is in anOFF state.
 7. The exhaust sampling system of claim 4, wherein saidcontroller allows flow of said fill gas to said at least one collectionbag when the engine is in said ON state, and said controller selectivelyprevents the flow of said fill gas to said at least one collection bagwhen the engine is switched to an OFF state during said test phase. 8.The exhaust sampling system of claim 7, wherein said controllerselectively allows the flow of said fill gas to said at least onecollection bag during said test phase when the engine is in said OFFstate based on a comparison of (i) a collected volume of said exhaustgas and said fill gas and (ii) a desired volume.
 9. The exhaust samplingsystem of claim 1, wherein said source of exhaust gas includes a mixtureof exhaust gas from the engine and said diluent gas when the engine isin said ON state.
 10. The exhaust sampling system of claim 1, whereinsaid controller operates in said first state when the engine is in saidON state and operates in said second state when the engine is in an OFFstate.
 11. The exhaust sampling system of claim 1, further comprising abackground collection unit including at least one background samplingbag.
 12. The exhaust sampling system of claim 11, wherein said source ofexhaust gas includes a mixture of exhaust gas from the engine and saiddiluent gas, said background collection unit collecting said diluentgas.
 13. The exhaust sampling system of claim 1, wherein said controllerdetermines said extraction rate during said test phase based on the timeduring said test phase at which the engine is switched to said ON staterelative to a predetermined time period of said test phase.
 14. Theexhaust sampling system of claim 13, wherein said test phase has apredetermined total time period and said controller determines saidextraction rate of said sample probe based on the first point in time atwhich the engine is switched to said ON state during said test phaserelative to said predetermined total time period of said test phase. 15.The exhaust sampling system of claim 1 wherein: said source of exhaustgas is a dilution tunnel in which said exhaust gas is diluted with saiddiluent gas; said controller permits the flow of said diluted exhaustgas from said sample probe to said at least one collection bag at saidextraction rate when the engine is in said ON state; and said controllerselectively prevents the flow of said diluent gas from said sample probeto said at least one collection bag when the engine is in an OFF stateduring said test phase.
 16. The exhaust sampling system of claim 15,wherein said controller selectively permits the flow of said diluent gasfrom said sample probe to said at least one collection bag at saidextraction rate when the engine is in said OFF state during said testphase.
 17. The exhaust sampling system of claim 15, wherein saidcontroller selectively permits the flow of said diluent gas from saidsample probe to said at least one collection bag at said extraction ratewhen the engine is in said OFF state during said test phase based on acomparison of (i) a volume of said exhaust gas and said diluent gascollected in said at least one collection bag and (ii) a desired volume.18. An exhaust sampling system for an engine, the exhaust samplingsystem comprising: a dilution tunnel in which exhaust gas from theengine is diluted with a diluent gas; an exhaust collection unitincluding at least one collection bag that selectively receives saiddiluted exhaust gas; a sample probe in fluid communication with saiddilution tunnel and operable to selectively supply said at least onecollection bag with said diluted exhaust gas during a test phase; afirst flow path in fluid communication with said sample probe and saidexhaust collection unit; a source of fill gas; a second flow path influid communication with said source of fill gas and said exhaustcollection unit, wherein at least a portion of said second flow path isdifferent than said first flow path; and a controller operable to permitflow of said diluted exhaust gas from said sample probe to said at leastone collection bag in a first state and operable to prevent flow of saiddiluent gas from said sample probe to said at least one collection bagin a second state, said controller selectively supplying said dilutedexhaust gas to said at least one collection bag through said first flowpath during said test phase, said controller selectively supplying saidfill gas to said at least one collection bag through said second flowpath during said test phase.
 19. The exhaust sampling system of claim18, wherein said controller supplies said fill gas to said at least onecollection bag based on an ON time of the engine.
 20. The exhaustsampling system of claim 18, wherein said controller supplies said fillgas to said at least one collection bag based on a time during said testphase at which the engine is switched to an ON state.
 21. The exhaustsampling system of claim 20, wherein said test phase has a predeterminedtotal time period and said controller supplies said fill gas to said atleast one collection bag based upon the first time at which the engineis switched to an ON state during said test phase relative to saidpredetermined total time period of said test phase.
 22. The exhaustsampling system of claim 18, further comprising a valve associated witha sample probe and movable between an open state permitting flow of saidexhaust gas to said at least one collection bag and a closed statepreventing flow of said exhaust gas to said at least one collection bag,said controller in communication with said valve and operable to controlmovement of said valve between said open state and said closed state.23. The exhaust sampling system of claim 22, wherein said open state isa fully open state, said valve movable into one of a plurality ofpartially open states between said fully open state and said closedstate.
 24. The exhaust sampling system of claim 18, further comprising abackground collection unit including at least one background samplingbag.
 25. The exhaust sampling system of claim 24, wherein saidbackground collection unit collects said diluent gas.
 26. The exhaustsampling system of claim 25, wherein said background collection unitcollects said diluent gas during said test phase.
 27. The exhaustsampling system of claim 18, wherein said controller allows flow of atleast one of said diluent gas and said fill gas to said at least onecollection bag when the engine is in an ON state, and said controllerselectively prevents the flow of said diluent gas and said fill gas tosaid at least one collection bag when the engine is switched to an OFFstate during said test phase.
 28. The exhaust sampling system of claim27, wherein said controller selectively allows the flow of at least oneof said diluent gas and said fill gas to said at least one collectionbag during said test phase when the engine is in said OFF state based ona comparison of (i) a collected volume of said exhaust gas and said fillgas and (ii) a desired volume.
 29. The exhaust sampling system of claim27, wherein said controller prevents flow of said diluent gas and saidfill gas to said at least one collection bag during said test phase whenthe engine is in said OFF state during said test phase if a period thathas elapsed since a start of said test phase while said engine is insaid OFF state is less than a predetermined period.
 30. The exhaustsampling system of claim 29, wherein said controller allows flow of atleast one of said diluent gas and said fill gas to said at least onecollection bag during said test phase when the engine is in said OFFstate if said elapsed period is greater than or equal to saidpredetermined period.